1. Field of the Invention
The present invention relates to a method of treating spent electrolyte produced from electrolytic copper production to remove copper, arsenic, antimony, bismuth, nickel and the like therefrom.
2. Description of the Prior Art
In a general refining of copper concentrate, the copper concentrate is smelted within a series of furnaces to give an intermediate matte, which is then treated in a converting furnace to give a blister copper. The blister copper is purified in a purification furnace to remove sulfur and oxygen. Since thus purified crude copper still contains impurities and valuable metals, it is further purified by electro refining to give a pure copper, which is called as an electrolytic copper. The refining has an advantage that a removal of impurities and recovery of valuable metals are easy.
In electro refining of copper wherein a solution of copper sulfate containing a large amount of free sulfuric acid is served as an electrolyte, a plate of crude copper containing impurities is served as an anode, and a seed plate of pure copper is served as a cathode, copper is dissolved at the anode and deposited onto the cathode with a purity of 99.99% or more.
When copper is dissolved, various impurities such as arsenic, nickel, antimony, bismuth and the like are also dissolved and accumulated in the electrolyte, resulting in a deterioration of the pure copper quality and a significant decrease in a current efficiency. Accordingly, it is required that a part of the electrolyte is periodically taken from the cell and purified to remove impurities so as to maintain the concentration of impurities below a certain level.
One common method for carrying out such purification of spent electrolyte is an electro winning, wherein the spent electrolyte is electrolyzed by using a copper as a cathode and insoluble lead as an anode to deposit copper and arsenic contained in the solution onto the copper cathode.
However, the method has some disadvantage that since arsenic deposits containing a large amount of copper and arsenic is formed as a by-product, retreatment is unavoidable to recover copper values therefrom and a toxic gas is generated during operation to cause an environmental pollution.
Therefore, there have been attempts to provide a new method of treating a spent copper-refining electrolyte with a low installation and operation costs without problems of a formation of arsenic deposits and a pollution.
For example, U.S. Pat. No. 4,404,071 discloses a method for treating spent electrolyte by using a hydrogen sulfide gas. The method comprises the steps of: pre-treating the spent electrolyte from the cell to remove copper until the copper content is 5-20 g/l, blowing a hydrogen sulfide gas into the pre-treated solution to precipitate metal ions including copper, arsenic, antimony and bismuth in the form of sulfides. The filtrate is returned to the cell and the precipitated sulfide is retreated in the smelting process.
However, this method has disadvantages that if the spent electrolyte contains a large amount of nickel, which is not removed by a hydrogen sulfide gas, the filtrate can not be returned to the electrolytic cell as well as the arsenic, antimony and bismuth precipitates as sulfides are returned along with copper to and recycled in the smelting process. The higher the concentration of impurities in the spent electrolytic solution is, the worse the problem is.
Accordingly, there has been a need to develop an effective method for thoroughly removing impurities from the electrolysis in the copper smelting industry.